2018-06-24 11:19:30
Numerous liver diseases are associated with imbalances in the bacterial species of the intestinal flora. For this reason, some scientists have suggested that liver cancer could be affected by alterations in the flora. In fact, the liver contains numerous cells of the immune system and it has been shown that the composition of the intestinal flora affects the results of immunotherapy treatments against liver cancer.
The reason that can help explain the above facts is that 75% of the blood supply to the liver comes from the portal vein, which collects and transports to this organ the blood that previously irrigated the intestine. In this way, the substances produced or metabolized by the intestinal flora pass into the blood and are thus transported to the liver. One of these substances are bile acids, fundamental components of bile.
Bile is a yellowish-green fluid produced by the liver and stored in the gallbladder, from where it is secreted into the intestine to help emulsify and digest fats. Additional studies indicated that metabolic products of bile acids produced by the flora could contribute to the development of liver cancer.
To clearly determine whether gut flora affects tumor growth, researchers treat animals with a combination of three antibiotics that kill much of their flora. Under these conditions, the mice reduced the growth of tumors and metastases that developed in the liver, but did not decrease the growth of tumors that the scientists had induced to grow in other parts of the body. Thus, it seems clear that the intestinal flora favors tumor growth in the liver, if a tumor develops in this organ.
By studying the immune cells present in the liver of mice with liver tumors, the scientists found that the intestinal flora affects the presence and activity of the so-called natural killer (NK) cells, which are the most important in immunosurveillance against cancer, because they are capable of killing tumor cells. By eliminating the flora with antibiotics, NK cells increase their presence and activity in the liver, which contributes to reducing tumor growth.
The researchers knew that these cells go to the various organs when they detect a particular molecule produced by the cells of the blood vessels. The elimination of the flora increased the production of this molecule in the blood vessels of the liver, which led to a greater number of NK cells going to that organ.
Why was this molecule produced in greater quantity by eliminating the flora? The researchers determine that the metabolic products of the bile acids generated by the intestinal flora are responsible for decreasing the production of this molecule. It remains to be clarified whether something similar happens in humans.
Referencia: Chi Ma et al. Gut microbiome-mediated bile acid metabolism regulates liver cancer via NKT cells. Science. May 25, 2018. DOI: 10.1126/science.aan5931.
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